The contamination or dilution of lubricating engine oils in internal combustion engines such as biodiesel engines has been a concern. Biodiesel fuels comprise components of low volatility which are slow to vaporize after injecting into the cylinders of the biodiesel engine. This may result in an accumulation of these components of low volatility on the cylinder wall where they can be subsequently deposited onto the crankshaft by the action of the piston rings. Because biodiesel fuels generally have low oxidative stability, these deposits on the cylinder wall or in the crankshaft can degrade oxidatively and form polymerized and cross-linked biodiesel gums, sludges or varnish-like deposits on the metal surfaces that may damage the biodiesel engine or the crankshaft. Furthermore, biodiesel fuels and resulting partially combusted decomposition products can contaminate the engine's lubricants. These biodiesel contaminants further contribute to the formation of oxidization of the engine oil, deposit formation, and corrosion, particularly of lead and copper based bearing material. The influence of biodiesel on the engine oil may require improved additives formulations to address oxidation, corrosion, and deposits within the engine.
Generally the gums, sludges or deposits can be minimized by using a lubricating oil composition. However, lubricating oil compositions generally comprise a base oil which can also be oxidized under the extreme conditions while lubricating the running parts of an internal combustion engine. Therefore, there is always a need to protect the base oils from oxidative deterioration. Further, there is also a need to protect the biodiesel fuel from oxidation.